Contaminants, such as hazardous, polluting or toxic materials or wastes, are a problem for the United States and for countries world-wide. Governmental agencies, commercial companies, the military, and consumers are searching for more cost-effective technologies that can be used to remove these hazardous and polluting materials.
Contaminants are continuously produced by activities of humans on the planet. In addition, natural causes can release or create contaminants in the environment. Oil and radioactive elements are naturally released into the environment and natural disasters, such as floods, create polluted areas in their wake. In addition to the on-going production of waste materials, there is a large amount of contaminants from activities in the past. Many of these past activities were not regulated by concerns for effects on the environment, and thus there are environmental problems dating back years or decades which require remediation.
The costs of cleaning up the environment are staggering. These costs are a drain on the economies of thriving countries and are an almost insurmountable problem for poorer countries. Many of the current technologies for removing hazardous or contaminating wastes from the environment involve sophisticated machinery or personnel, all of which add to the costs.
There are governmental attempts in the United States for correcting some of these environmental problems, such as the Superfund and Resource Conservation and Recovery Act, RCRA. In addition to legislative pressure for remediation, many commercial companies are interested in remediation. Not only are the companies compelled by the governmental regulations to stop adding hazardous materials to the environment and to clean up the existing hazards, but many states have prohibited the sale of real property unless the liability for any contamination discovered and any cleanup necessary is delineated. Additionally, consumers and members of the population who may be exposed to and harmed by the contaminants are creating pressure to remove pollutants from their environment. Therefore, there is a need by the government, by business entities, and by consumers for compositions and methods which can remove contaminants from the environment.
In the past, contaminants were contained by placing them in landfills or land treatment options. New technologies are now necessary because the costs of utilizing land as a holding site is too expensive or is prohibited by current regulations. Many of the contaminants thought to be isolated in landfills were found to be leaching into the surrounding environment, and thus were not "isolated" in the landfill. Companies now have to decontaminate millions of cubic yards of contaminated soil and millions of gallons of contaminated groundwater that cannot be placed in a landfill or incinerated because the costs are too high. Therefore, inexpensive methods and compositions are needed to decontaminate these materials.
Current methods of waste treatment are not adequate for remediating the contaminated air, soil or water by removing the contaminants. Physical methods such as adsorption, filtration or extractions are effective for some wastes. Unfortunately, additional treatments are often required to complete the decontamination because these treatments merely separate out the wastes but do not destroy the waste by converting it into a nonhazardous form. Chemical treatment can be used on some wastes, but there may be hazardous by-products or sludges produced by treatment. Wastes may be isolated or altered through methods such as stabilization, solidification or encapsulation, but the waste is merely contained, not destroyed. Additionally, the problem of storage of the contained waste is created.
Incineration is one effective method for reducing the volume of wastes and completely destroying the waste. Incineration is an expensive method and requires a large consumption of energy resources to remove the wastes. The gaseous emissions and toxic ash that result from the incinerator are new sources for contaminants in the environment. Additionally, consumers fear that operating incinerators will contaminate the environment with the by-products of the incinerator.
Biological treatment is another method of remediation that has been used for decades in wastewater treatment and composting processes. Such processes also produce sludges and wastewater that may require further treatment and disposal. There are many applications for biological treatments of hazardous wastes, but there are many engineering problems which must be overcome for biological systems to work efficiently to degrade and convert the hazardous materials.
Bioremediation occurs naturally at a low level and a very slow rate, even under ideal situations, in the biodegradation of material and wastes. Technologies using bioremediation methods take advantage of the naturally present degradative organisms to decontaminate air, soil or water. Currently, bioremediation methods fall into three broad categories-land treatment, bioreactors, and in situ treatment.
In land treatment, the contaminated materials are mixed into surface soils or composted. These systems require the addition of bulking agents, aeration systems, water and nutrients to enhance the actions of the biological organisms.
Bioreactors are another means for bioremediation of contaminated materials. Lagoons, ponds, tanks or reactors with bacterial growth, are designed to decontaminate groundwater or such mixtures as slurries of soil and water. These methods may require that the contaminated water or slurry to be excavated, pumped or trucked to a distant site where the bioreactor is located. Additionally, the soils may have to be handled and sorted. After treatment at the bioreactor, any incompletely cleaned water or slurry would have to be transported elsewhere.
Transportation of hazardous wastes involves another set of regulations and requirements that can be expensive. Once in an ex situ reactor, the water or slurry has to be effectively mixed and aerated. Additionally, the growth of the bacteria in reactor must be controlled by controlling the residence time or the bacteria with the contaminated material, nutrient levels, temperature, pH, and concentration. If a batch process is used, only a limited amount of water or slurry can be decontaminated. These types of bioreactor systems are costly because of the capital, maintenance and operating expenses involved in running it.
On-site usage of bioreactors can eliminate the cost of trucking the material to the bioreactor, but the cost of excavation or handling of the soils is still present. These are generally not insignificant costs. In addition, the site may not lend itself to the presence of a bioreactor or support for the personnel necessary to oversee the reactor.
Another type of bioremediation, in situ remediation, utilizes the growth of indigenous, contaminant-degrading microorganisms which are present at the contaminated site. These organisms are present at the site and are capable of some kind of degradation of a contaminant. Unfortunately, their decontaminating action proceeds at too low a level and too slow a rate to effectively decontaminate the area. Additionally, the organisms may be only able to chemically change one contaminant in a mixed collection of pollutants, or only make a few chemical changes in a chemically-complex contaminating molecule. The growth of the naturally occurring microorganisms must be enhanced by the addition of oxygen and nutrients.
A major problem with in situ treatment using indigenous microorganisms is that the conditions of the site cannot be controlled like those of the bioreactor. This lack of control of such conditions as temperature, pH, and nutrient levels leads to a much longer time for decontamination of the site. It is also much harder to predict what the outcome of the treatment will be, how long the decontamination will take, and how the contaminants will be changed and how much will be changed.
Usually contaminated sites are contaminated by more than one kind of hazardous or polluting material. There is usually a mixture of several types of contaminants or several breakdown products of one contaminant. Currently, the number of contaminants which can be degraded by biological treatments is limited to a few organics and the processes are extremely sensitive to environmental conditions.
Therefore, what is needed are compositions and methods that can perform bioremediation within a contaminated or polluted site that is inexpensive, can be installed in the area without extensive structures or personnel to support it, and can be applied to a wide variety of environments. Even more ideally, would be a bioremediation system that would not only remove or stabilize the contaminated wastes, but could also convert the wastes into usable products such as energy sources or growth promoters. Such a biosystem could also be used to generate the beneficial products such as energy or growth promoters under conditions which promote the production and not only in waste treatment. Bioremediation systems which could clean up sites contaminated by a mixture of contaminants are also needed because very few sites are contaminated by only one contaminant. A bioremediation system that can clean up sites contaminated by both metals and organic materials is needed.